Multiple sensor ultrasonic monitoring device

ABSTRACT

An ultrasonic monitoring apparatus is provided for use by an operator in detecting ultrasonic vibrations and sound waves. The ultrasonic monitoring apparatus consists of a hand held device with a sensor socket that allows a variety of different types of sensors to be interchangeably installed in the hand held device. These sensors include both contact and airborne ultrasonic sensors as well as a combination temperature and ultrasonic sensor that allows the operator to simultaneously monitor the surface temperature of an object and the ultrasonic vibrations produced by the object. Identification information corresponding to the type of sensor is encoded on the individual sensors. The identification information is read by an identification circuit located in the hand held device. This identification information allows the hand held device to configure itself to operate with the type of sensor installed in the socket.

This application is a continuation of application Ser. No. 09/073,564filed May 6, 1998, now abandoned.

BACKGROUND

1. Field of the Invention

In general, the present invention relates to a device for detecting andmonitoring ultrasonic sound waves. In particular, the present inventionrelates to a portable ultrasonic monitoring instrument that utilizesmultiple sensors which can be interchangeably installed into a sensorsocket to obtain measurements such as ultrasonic sound wave strength andsurface temperature that are useful in detecting machinery defects andequipment failures.

2. Background of the Invention

The normal frequency range for human hearing is roughly 20 to 20,000hertz. Ultrasonic sound waves are sound waves that are above the rangeof human hearing and, thus, have a frequency above about 20,000 hertz.Any frequency above 20,000 hertz may be considered ultrasonic. Mostindustrial processes, including almost all sources of friction, createsome ultrasonic noise. For example, leaks in pipes, machinery defectsand electrical arcing produce ultrasonic sound waves that have afrequency that is too high for the human ear to detect. In the past,analog ultrasonic sensors have been used in industrial settings to sensethese ultrasonic sound waves. To monitor the ultrasonic sound wavesproduced by operating machinery, an operator would use an ultrasonicsensor to obtain a reading indicating the strength of the ultrasonicsound waves near the machine. If the ultrasonic sound levels generatedby one machine were larger than those produced by another similarmachine, the operator would investigate further to determine if aproblem existed with the noisy machine. If the ultrasonic sound levelswere approximately equal to those produced by a properly functioningmachine, the operator would assume the machine was properly functioningand simply proceed to the next machine. Some of the prior art ultrasonicsensors used to monitor machines were semi-permanently mounted onindividual machines so that ultrasonic readings could be obtained bysimply checking the output of the ultrasonic sensors. However, otherultrasonic detectors were portable to allow the operator to monitor manymachines. These portable ultrasonic detectors were especially useful inlocating small leaks in pipes carrying pressurized gasses. Becauseultrasonic sound waves attenuate very rapidly, the location of the soundwaves is usually the location of the leak. Therefore, in order to locatea leak, the user simply moved the ultrasonic detector over the surfaceuntil the strength of the ultrasonic sound waves rapidly increased. Theuser then investigated further by placing soapy water on the locationwhere it was suspected that there was a leak. If a leak was present,bubbles would form in the soapy water where the gas was escaping.

These analog ultrasonic instruments suffer from many drawbacks. Forexample, the analog instruments do not provide a quantitativelyreferenced power level of the signal to the user. Instead, the analogultrasonic units simply provide a relative indication of the ultrasonicsound waves' strength in one location compared to another location.Typically, this information is provided to the user by a needle on adial with an adjustable volume. The volume is set so that the needle isat a reference point when an ultrasonic measurement is taken in aparticular location. If the needle rises above that point when a readingis taken in another location, the ultrasonic noise level is higher atthe second location than the reference point and vice versa This isundesirable because it makes it difficult to compare readings taken atone point in time to readings taken at a later point in time. Also,prior art analog instruments did not employ analog to digital convertersor microprocessors, making it difficult for them to perform advancedsignal analysis techniques on the ultrasonic electrical signals.

SUMMARY OF THE INVENTION

The present invention solves the foregoing problems by providing anautomated ultrasonic monitoring system that utilizes multiple sensors todetect ultrasonic sound waves. The sensors can be removably installed ina sensor socket. Each sensor contains encoded identification informationthat allows the ultrasonic monitoring system to recognize the type ofsensor installed in the socket and configure itself to operate with thesensor. This ability to recognize new sensors allows the ultrasonicmonitoring system to be upgraded by simply developing new sensors andinstalling new firmware to identify the new sensors. Thus, the presentinvention is a substantial improvement over the prior art.

In accordance with the present invention, a portable ultrasonic soundand temperature detection and analysis device for measuring surfacetemperatures and detecting ultrasonic sounds produced by sources such asleaks in pipes, arcing, electrical corona and machinery defects isprovided. The ultrasonic device comprises an elongate housing forenclosing the ultrasonic device. The elongate housing further has a gripthat is designed to provide a handle that allows a user to carry andpoint the ultrasonic device like a pistol. A barrel shaped portion isattached to the grip at one end. A trigger which is used to control thefunctioning of the ultrasonic device is located at the junction of thebarrel shaped portion and the grip.

The invention uses a set of sensors to produce ultrasonic electricalsignals. The set of sensors includes at least a temperature sensor, anultrasonic sensor, and a combination temperature and ultrasonic sensor.A plurality of electrical contact pads are located on a cylindrical baseportion of each sensor in the set of sensors. Identification andconfiguration information concerning the type of sensor is encoded oneach sensor in the set of sensors. An identification circuit receivesand analyzes the identification and configuration information from thesensor installed in the sensor socket and configures the ultrasonicmonitoring device to operate with the sensor installed in the sensorsocket. The sensor socket is located in the barrel shaped portion of theultrasonic device and is designed to interchangeably receive a sensorfrom the set of sensors. The sensor socket has a cylindrical shapedcavity with walls and a bottom portion for receiving the sensor from theset of sensors. A set of pins located in the bottom portion of thesensor socket provide electrical contacts between the plurality ofelectrical contacts on the sensor installed in the sensor socket and theultrasonic device. A pair of spaced apart L-shaped grooves are locatedin the walls of the cylindrical shaped cavity. Each of the L-shapedgrooves has an open receiving portion that begins at the rim of thecylindrical shaped cavity and extends a distance down the cavity wallsto an ending position and a leg portion that extends perpendicularlyfrom the ending position of the open receiving portion. A pair ofprotrusions are fixedly attached to the sides of each of the sensors inthe set of sensors. The protrusions are shaped and positioned to bereceived in the L-shaped grooves in a manner that removably secures thesensor in the sensor socket. Installation guide means prevent a sensorfrom the set of sensors from being improperly installed in the sensorsocket. Focusing means may be used to focus the area from which thesensors can receive ultrasonic vibrations.

The ultrasonic monitoring device is preferably powered by a rechargeablepower supply located in the grip of the elongate housing that provides apower supply voltage and a ground voltage to the ultrasonic device. Abattery charger jack located underneath the barrel shaped portion of theelongate housing receives a voltage that is used to recharge therechargeable power supply.

The present invention further includes a variable frequency sine waveoscillator that produces local oscillator frequency signals. A mixerreceives the ultrasonic electrical signals from the sensor installed inthe sensor socket and the local oscillator frequency signals from thevariable frequency sine wave oscillator and heterodynes the ultrasonicelectrical signals to produce audible frequency range signals thatcorrespond to the ultrasonic electrical signals but are in the audiblefrequency range of a human being. A low pass filter receives the audiblefrequency range signals from the mixer and removes any above audiblefrequency range signals in the audible frequency range signals receivedfrom the mixer. A headphone jack located on the base of the gripreceives the audible frequency range signals from the low pass filter. Apair of headphones have a headphone plug that receives the audiblefrequency range signals from the headphone jack when the headphone plugis inserted into the headphone jack and broadcasts the audible frequencyrange signals so that they can be heard by a user of the ultrasonicdevice.

Additional features of the present invention include a temperature sensecircuit that supplies a constant current to a sensor installed in thesensor socket. A temperature signal is produced that corresponds to thetemperature sensed by the installed sensor. The temperature signal issupplied to a microprocessor which interprets the temperature signal asa temperature. A display is provided that displays the temperature valueto the operator of the ultrasonic monitoring device. A communicationsport allows the ultrasonic monitoring device to communicate thetemperature and other sensed values to an external device.

Thus, the present invention overcomes the problems associated withsingle sensor prior art devices. The provision of sensor socket adaptedto interchangeably receive a plurality of sensors allows one ultrasonicdevice to be configured to perform a wide variety of monitoring tasks.Sensors tuned to receive ultrasonic sound waves of different frequenciescan be installed in the socket without requiring extensivemodifications. In addition, the provision of a combination temperatureand ultrasonic sensor allows multiple measurements to be takensimultaneously.

In a particularly preferred embodiment of the present invention, thesensor socket is a cylindrical shaped cavity having walls and a bottomportion for receiving a sensor from a set of sensors. A set of pinslocated in the bottom portion of the sensor socket provide electricalcontacts between the plurality of electrical contacts on the sensorinstalled in the sensor socket and the ultrasonic monitoring device. Apair of spaced apart L-shaped grooves are located in the walls of thecylindrical shaped cavity. Each of the L-shaped grooves has an openreceiving portion that begins at the rim of the cylindrical shapedcavity and extends a distance down the cavity walls to an endingposition and a leg portion that extends perpendicularly from the endingposition of the open receiving portion. A pair of protrusions arefixedly attached to the sides of each of the sensors in the set ofsensors wherein the protrusions are shaped and positioned to be receivedin the L-shaped grooves in a manner that removably secures the sensor inthe sensor socket. The open receiving portions of the L-shaped groovesare positioned so that the sensors will always be installed in thesocket with the same orientation.

In further accordance with the particularly preferred embodimentdiscussed above, output means output properties of the ultrasonicelectrical signals and identification information concerning the sensorinstalled in the sensor socket. One of the sensors in the set of sensorsis an ultrasonic waveguide probe that senses ultrasonic vibrations bybeing placed in contact with the object producing the ultrasonicvibrations and one of the sensors is an airborne ultrasonic sensor thatsenses ultrasonic vibrations being produced by an object without cominginto contact with the object. The ultrasonic sensors have apiezoelectric element for converting ultrasonic vibrations intoultrasonic electrical signals corresponding to the ultrasonicvibrations. A cone may be fit over a sensor in the set of sensors asneeded to focus the area in which the sensor detects ultrasonic soundwaves. Preferably, at least one ultrasonic sensor is substantiallyresonant at 40 kHz. However, the present invention also comprehends anultrasonic sensor that has a resonant frequency that can be adjusted toone of a plurality of resonant frequencies. Such an ultrasonic sensorincludes a tuneable inductive and capacitive circuit having anadjustable resonant frequency.

Also in accordance with the present invention, analysis means performtime and frequency domain waveform analysis on the ultrasonic electricalsignals. This analysis mainly consist of digitally performing fastFourier transforms on the signals to produce frequency spectrums.Regions of the frequency spectrum are then examined to locate peaks andpatterns occurring at frequencies that would tend to indicate amachinery defect. The exact frequencies would depend upon the speed atwhich the particular machine was operating. This is the type of machinespecific data that would be included in the configuration informationprovided to the ultrasonic sensing device. Alarm means are used toinform the operator of the device when a property of an ultrasonicsignal exceeds a user selected threshold value.

An especially preferred embodiment of the present invention furtherprovides a combined ultrasonic sound wave and temperature sensor. Ahousing encloses the ultrasonic sound wave and temperature sensor. Anultrasonic sensor attached to the housing senses ultrasonic vibrationsproduced by an object and a temperature sensing means measures thesurface temperature of an object. The temperature sensing means has acontact tip constructed out of a material having a high thermal andultrasonic conductivity and a temperature sensing element that isconstructed out of a material with a resistance that is highly dependentupon the temperature of the material. An attachment means of highthermal conductivity and low electrical conductivity couples thetemperature sensing element to the contact tip. In an alternativeembodiment, the temperature sensor may be a thermocouple temperaturesensor. The temperature sensing means is coaxially mounted inside theultrasonic waveguide probe. An insulating bushing is mounted inside theultrasonic wave guide probe so that the insulating bushing surrounds thecontact tip of the temperature sensing means. In an especially preferredembodiment, the insulating bushing is constructed out of Dupont Vespel.The materials for the contact tip and the temperature sensing elementare selected to minimize the intrinsic thermal time constant of thetemperature probe.

Other objects, features and advantages of the present invention willbecome apparent by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings below, like reference characters refer to like partsthroughout the several views, and wherein:

FIG. 1 is a perspective view of an operator using the ultrasonicmonitoring system of the present invention;

FIG. 2 is a side view of the elongate housing that shows the locationsof the main internal components;

FIG. 3 is a front view of the elongate housing that shows the bottom ofthe sensor socket;

FIG. 4 is a bottom view of the barrel shaped portion of the elongatehousing that shows the location of the input and output ports.

FIG. 5 is a bottom view of the grip portion of the elongate housingshowing the headphone jack;

FIG. 6 is a rear view of the elongate housing that shows the display anduser input keys;

FIG. 7a is a block diagram of the electronics contained in the elongatehousing;

FIG. 7b is a block diagram of an embodiment of a received signalstrength indicator;

FIGS. 8a and 8 b are pictorial representations of a preferred sensorsocket;

FIGS. 9a, 9 b, and 9 c are pictorial representations of an airbornesensor;

FIGS. 10a, 10 b, 10 c, and 10 d are pictorial representations of acontact sensor;

FIG. 11 is a pictorial representation of a focusing cone;

FIG. 12 is a pictorial representation of a method for using theultrasonic transmitter to locate a hole in a pipe; and

FIG. 13 is a flow chart outlining a route based method of monitoringequipment using the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The ultrasonic monitoring system of the present invention effectivelylocates leaks of air, steam, or other gases from pressurized systems aswell as arching and electrical corona, which may produce ultrasonicsounds. Furthermore, the ultrasonic monitoring system can also diagnoseand analyze steam trap operation, bearing and gear defects, cavitationand surging in pumps and compressors, lubrication problems in dynamicequipment, valve operation, steam lines, and piston friction anddetonation problems in reciprocating equipment.

Referring now to FIG. 1, an especially preferred ultrasonic monitoringsystem 10 for detecting and monitoring ultrasonic sound waves 12 isshown. The ultrasonic sound waves 12 are emanating from the intersection14 of two abutting pipes 16 and 18. In the case of leak detection, theultrasonic monitoring system 10 is principally used by the operator 20to determine the location from which the ultrasonic sound waves 12 areemanating. The ultrasonic monitoring system 10 consists of an ultrasonicsensor 22 mounted in a portable elongate housing 24. In operation, theelongate housing 24 is held by the operator 20 and pointed toward amachine or device that might contain a leak or defect that is radiatingultrasonic sound waves 12. A pair of headphones 26 are worn by theoperator 20 and attached to the elongate housing 24 via a cord 28. Theoperator 20 of the ultrasonic monitoring system 10 receives an audiblesignal the volume of which indicates the relative strength of theultrasonic sound waves 12 being received by the sensor 22 located in thebarrel of the elongate housing 24 through the pair of headphones 26.When the elongate housing 24 and the sensor 22 are pointed away from thesource 14 of the ultrasonic sound waves 12, the strength of theultrasonic sound waves 12 detected by the sensor 22 decreases. When theelongate housing 24 and the sensor 22 are pointed toward the source 14of the ultrasonic sound waves 12, the strength of the ultrasonic soundwaves 12 detected by the sensor 22 increases. This increase and decreasein the detected ultrasonic sound wave strength can be audiblyrepresented in a variety of fashions. For example, a rise in the volumeof a tone produced by the ultrasonic monitoring system 10 could indicatethe detected ultrasonic sound waves are growing stronger and a fall inthe volume of the tone could indicate the sound waves are growingweaker. A rise and fall in the pitch of the tone could also indicate arespective rise and fall in the strength of the detected ultrasonicsound waves. Alternatively, a Geiger counter type clicking would alsoserve the function of indicating the strength of the detected soundwaves to the user 20 of the ultrasonic monitoring system 10. However, ina most preferred embodiment, the ultrasonic sound waves 12 received bythe sensor 22 are heterodyned to produce related electrical signals thathave a frequency in the audible range of humans. These related signalshave many of the distinctive properties of the ultrasonic sound waves 12from which they were produced. Providing these related electricalsignals to the headphones 26 allows the operator 20 to identify the typeof noise source radiating the ultrasonic sound waves 12 by listening tothe distinctive noise signals created by different types of ultrasonicsound wave sources.

The ultrasonic sound waves 12 received by the sensor 22, or the dataderived from the ultrasonic electrical signals produced by the sensor22, are preferably stored in a microprocessor based system 32, which isreleasably secured to the operator 20. The microprocessor based system32 is used to store and analyze the data collected by the ultrasonicmonitoring system 10, provide testing information to the operator 20 andprompt the operator 20 to take measurements from particular locations.As discussed in greater detail below, the microprocessor based system 32in a preferred embodiment is a portable personal computer or personaldata assistant. The microprocessor based system 32 is secured to theoperator 20 via a utility belt 30. The utility belt 30 also has aholster for receiving the elongate housing 24, pockets for accessoriessuch as small tools, tags, survey tape and soap solutions, and anultrasonic sound wave transmitter and charger 34.

The elongate housing 24 contains many of the components needed toimplement an ultrasonic monitoring device 10 in accordance with thepresent invention. The preferred internal location of these componentsinside the elongate housing 24 is shown in FIG. 2. A sensor socket 36 islocated in the barrel portion 38 of the elongate housing 24. The sensorsocket 36 is designed to receive a variety of different sensors 22. Whena sensor 22 is installed in the sensor socket 36, the sensor socket 36provides electrical contact between the installed sensor 22 and amicroprocessor based control circuit 40 also located in the barrelportion 38 of the elongate housing 24.

As shown in FIG. 3, the electrical contacts between the sensor 22 andthe sensor socket 36 are provided by a series of electrical contacts 42located in the sensor socket 36. In an especially preferred embodiment,the electrical contacts 42 consist of six spring biased pins 42 thatcreate an electrical connection between the pins 42 and correspondingcontact pads 108 located on the base of the sensors 22. The sensorsocket 36 is surrounded by a plate 44 that covers and protects the frontof the barrel portion 38 of the elongate housing 24.

The microprocessor based control circuit 40 is internally contained inthe barrel portion 38 of the elongate housing 24. Preferably, themicroprocessor 78 in the microprocessor based control circuit 40 is asixteen bit Toshiba microprocessor having model number TMP93CS41F. Themicroprocessor based control circuit 40 also preferably contains a RAMchip that is 256K×8 bits and a flash memory that is 64K by 8 bits. Themicroprocessor based control circuit 40 can communicate to externaldevices by means of several input and output ports located on the lowerportion of the barrel 38 of the elongate housing 24. As shown in FIG. 4,an RS 232 port 46 is located on the lower portion of the barrel 38. Inaddition to the RS 232 port 46, an infrared communications port 48 isalso located on the lower portion of the barrel 38 beneath the sensorsocket 36 and provides the microprocessor control circuit 40 the abilityto establish wireless communication with an external device. Preferably,the infrared communications port 48 is a low-voltage infrared receivermanufactured by Texas Instruments under Model No. TIR1000. Additionally,a signal output port 50 is located near the RS 232 port 46 and theinfrared communications port 48. The signal output port 50 provides asignal that is the detected envelope waveform of the ultrasonicelectrical signal. The detected envelope waveform signal consists of anyinstantaneous point on the detected waveform having a DC value directlyrelated to the signal strength in decibels at that point. This signaloutput may be provided to a machine analyzer so that frequency and timedomain analysis can be performed on the ultrasonic envelope waveform.The final port shown in FIG. 4 is a battery charger jack 52 that is usedto receive the DC voltage source that charges the rechargeable powersupply 58.

Referring back to FIG. 2, a trigger 54 for activating the ultrasonicmonitoring system 10 is located at the junction of the barrel portion 38and the grip portion 56 of the elongate housing 24. The trigger 54 ispositioned similar to a trigger on a real pistol and is electricallyconnected to the microprocessor control circuit 40. When the trigger 54is pressed, the ultrasonic monitoring system 10 begins collecting data.When the trigger 54 is released, the system 10 ceases collecting data.Thus, the trigger 54 simply functions as an activation switch and it isunderstood that there are alternative manners in which this functioncould be implemented.

The electrical components of the ultrasonic monitoring system 10contained in the elongate housing 24 are powered by a rechargeable powersupply 58 that is mounted in the grip portion 56 of the elongate housing24. As previously discussed, the rechargeable power supply 58 isrecharged by a way of a battery charger jack 52 which is located next tothe signal output port 50. A standard adapter having a first end forplugging into a common electrical outlet and a second end for engagingport 52 provides power to the battery chargerjack 52. A headphone jack62 located on the bottom portion of the grip 56 extends through thehandle plate 60 of the elongate housing 24. The headphone jack 62provides signals to the headphones 26 through a removable cord 28 thatis electrically connected to the headphones 26. Alternatively, wirelessheadphones may be incorporated into the present invention. FIG. 5 is aview of the bottom of the grip 56 that clearly shows the headphone jack62 and the handle plate 60.

FIG. 6 shows the rear plate 64 of the elongate housing 24 that containsthe display 66 that is viewed by the operator 20 when ultrasonic datameasurements are being taken. The display 66 is mounted in the rearplate 64 and provides visual ultrasonic data indicators and operationalinformation to the operator 20 of the ultrasonic monitoring system 10.The display 66 is preferably a 2×12 character matrix liquid crystaldisplay. A down arrow user input key 68, an up arrow user input key 70and a mode user input key 72 are located below the display 66. The grip56, the headphone jack 62 and the internal rechargeable power supply 58are also shown in FIG. 6.

The functioning of the electrical components inside the elongate housing24 can better be understood by examining a block diagram of thecomponents. The embodiment shown in FIG. 7a has a ultrasonic sensor 22with an integral temperature sensor 74 installed in the sensor socket36. In a preferred embodiment, the temperature sensor 74 is coaxiallymounted inside the cavity of the ultrasonic sensor 22. The ultrasonicsensor 22 with the integral temperature sensor 74 provides ultrasonicelectrical signals to the electrical contacts 42 in the sensor socket36. The sensor socket 36 provides the ultrasonic electrical signal thatis related to the strength of the ultrasonic sound waves 12 received bythe ultrasonic sensor 22 to a first voltage controlled amplifier 76. Theamount of amplification provided by the first voltage controlledamplifier 76 is controlled by a microprocessor 78. After beingamplified, the amplified ultrasonic electrical signal is sent to a mixer80. The mixer 80 mixes the amplified ultrasonic electrical signal withan oscillation signal provided by a microprocessor controlled variablefrequency sine wave oscillator 82 to produce a signal that is related tothe original ultrasonic electrical signal produced by the ultrasonicsensor 22. This signal consists of at least: (1) the amplifiedultrasonic electrical signal; (2) the oscillator signal; (3) thefrequency sum of the ultrasonic electrical signal and the oscillatorsignal; and (4) the frequency difference of the ultrasonic electricalsignal and the oscillator signal. The signal output from the mixer 80 ispassed through a low pass filter 84 to remove any high frequencycomponents above the audible frequency range of a human being. Thisfiltered signal is then sent to a second voltage controlled amplifier 86that is controlled by the microprocessor 78. Finally, the amplified andfiltered signal is sent to the headphones 26 where it is broadcast tothe operator 20. The point is to create a signal that can be heard byhumans and is related to the ultrasonic electrical signals in a mannerthat allows the operator 20 to distinguish between different ultrasonicelectrical signals by distinguishing between the different mixedsignals. The second voltage controlled amplifier 86 is essentially avolume control for the head phones 26.

An advantage of the ultrasonic monitoring system 10 of the presentinvention is that there are two signal paths for the ultrasonic electricsignals produced by the ultrasonic sensor 22. As discussed above, onesignal path provides an audio output that can be listened to by theoperator of the ultrasonic monitoring system 10. However, the ultrasonicelectrical signal received from the ultrasonic sensor 22 is also sent toa received signal strength indicator 90. The received signal strengthindicator 90 is a functional part of a Philips Semiconductor RFCommunications Products Model SA637 low-voltage IF receiver. Thisreceived signal strength indicator produces an envelope waveform of theultrasonic electrical signal consisting of instantaneous points on thewaveform having a DC value related to the signal strength in decibels ofthe ultrasonic electrical signal at that point.

Referring now to FIG. 7b, an embodiment of the received signal strengthindicator 90 is depicted. The signal from the sensor is received by anenvelope detector 93. A capacitor 94 and a resistor 95 provide theenvelope detector 93 with a rapid rise and slow decay output. In anespecially preferred embodiment, the envelope detector 93 is providedwith a response time constant of approximately 60 microseconds. The timeconstant is selected to substantially eliminate the intrinsic ultrasonicfrequency signals while allowing any dynamic amplitude variations inthose signals to be sent to microprocessor 78. The same signal is alsoprovided to output jack 50. Sampling of this envelope waveform allowsthe microprocessor 78 to calculate a referenced decibel level of theultrasonic sound waves at substantially any point in time. Thereferenced decibel level is determined by comparing the measured signalamplitude against a stored look up table of calibration values, a zerodecibel value being referenced to an acoustic sound pressure level of 20microPascals (0.0002 microBars) in an especially preferred embodiment.

The aforementioned envelope detection process could be referred to as apeak follower technique or, when used in conjunction with a filteringtime constant, as a form of demodulation. In addition, the envelopedetection process may be combined with an analog sample and holdcircuit, or, in an especially preferred embodiment, with an analog todigital converter. The technique provides an energy waveform of periodicbursts or rings that represents the bursts or rings of acousticvibrations. Depending upon the type of machinery faults generating them,these bursts may have a duration of a few milliseconds or less. Theintrinsic frequency of the bursts is relatively high, usually severalkHz or higher. In the case of the present invention, 40 kHz is thepreferred frequency of operation. The idea is to measure the peakamplitude of the burst or ring frequencies during sample time windows.In general, the intrinsic frequency or frequencies of the bursts are notof interest. It is the signal amplitudes and signal periodicity that areof the greatest interest for analysis. Nevertheless, the technique isstill of value with ultrasonic sound waves of constant amplitude andconstant duration, as may be the case with a steady leak from a pipe. Inthe case of a constant amplitude ultrasonic sound wave, the envelopewaveform would be a DC value representative of the decibel level of theultrasonic sound wave.

While we use envelope detection as shown in FIG. 7B, it is expresslyunderstood that the Peak Vue techniques disclosed in U.S. applicationSer. No. 08/840,844 filed Apr. 17, 1997 which is a continuation of U.S.application Ser. No. 08/555,296 filed Nov. 8, 1995 and now abandoned maybe used in accordance with an embodiment of the present invention. Bothtechniques perform a peak follower function and are able to capture peakamplitude values of short duration signal bursts or rings. Thus, itwould be possible to incorporate the Peak Vue method into the presentinvention.

Determining a referenced decibel output is a substantial improvementover the prior art method of using an analog instrument to provide arelative indication of the amplitude of the ultrasonic sound produced inone location compared to the ultrasonic sound produced at anotherlocation. Because there is no absolute reference for the prior artultrasonic measurements, it is difficult to compare a current reading toa prior reading taken at some earlier time. Furthermore, theunreferenced readings taken by one particular instrument are difficultto compare to the readings taken by another instrument. However, becausethe referenced decibel outputs of an instrument constructed inaccordance with the present invention are referenced to a known value,the referenced outputs of the present invention may be stored andaccurately compared to later readings obtained by other instruments.Thus, providing a referenced output allows measurements taken over anextended period of time to be analyzed to determine if the amount ofultrasonic sound produced by a particular machine is increasing ordecreasing.

The output from the integral temperature sensor 74 is provided to thetemperature sense circuit 92. In a preferred embodiment, the temperaturesense circuit 92 supplies a constant current to the temperature sensor74. The resistance of the temperature sensor 74 is dependent upon itstemperature. Thus, the voltage produced by the constant current flowingthrough the temperature sensor 74 is representative of the temperaturesensed by the temperature sensor 74. This voltage is provided to themicroprocessor 78 which interprets the voltage as a temperature andsends a temperature reading to the display 66.

The microprocessor 78 uses the signal indicative of the strength of thereceived ultrasonic sound waves to calculate a number of values. Thevalue calculated by the microprocessor 78 depends upon the mode in whichthe ultrasonic monitoring system 10 is operating. The operator 20 canselect from different operating modes by selecting the operating modemenu with the mode key user input 72 and then scrolling through the modemenu with the up 70 and down 68 arrow input keys. Once an operating modehas been selected by the operator 20, a symbol appears on the display 66indicating the mode in which the ultrasonic monitoring system 10 isoperating.

For example, if the user 20 selects the peak hold mode, the highestinput signal level received by the microprocessor 78 from the receivedsignal strength indicator 90 is retained and displayed as long as thetrigger 54 remains depressed. When the trigger 54 is released, the peakvalue of the signal received by the microprocessor 40 is frozen on thedisplay 66. The display 66 and the retained peak value are reset to zerowhen the trigger 54 is pressed again. Another mode which can be selectedis the instantaneous averaging mode. This is the preferred operatingmode of the present invention. In this mode, the microprocessor 78receives the signal indicative of the received ultrasonic electricalsignals strength and determines the strength of the ultrasonic soundwaves. In a similar fashion to that of the peak hold operating mode, themicroprocessor 78 retains and displays the strongest signal received.However, in the instantaneous mode of operation, this value is rapidlyreset. Preferably, the display 66 is updated at least three times asecond. This allows an almost instantaneous indication of the strengthof the ultrasonic sound waves being received by the ultrasonic sensor22. Yet another mode of operation is the averaged mode. In this mode,the microprocessor 78 calculates and sends to the display 66 an averagereferenced decibel level of the ultrasonic sound waves received betweenthe time the trigger 54 was pressed and the current time. When thetrigger 54 is released, the output is frozen. The decibel level isreferenced to an accepted standard, such as zero decibels at anacoustical sound pressure level of 20 micropascals or zero decibels at50×10⁻¹² inches peak to peak of mechanical displacement. Still anothermode of operation is the peak factor mode of operation. In accordancewith this mode, the difference between the peak value of the signal andthe average value of the signal is displayed. It is readily appreciatedthat a number of other values representing various characteristics ofthe sensed ultrasonic sound waves could be calculated by themicroprocessor 78. In fact, one of the primary advantages of using amicroprocessor based system is that the manner in which the digital datais analyzed and manipulated can easily be altered without requiringcomplex design changes. The particular values discussed are simply thoseof an especially preferred embodiment of the present invention.

The microprocessor 78 also allows an operator of the ultrasonicmonitoring system 10 to enter various information concerning the resultsof the ultrasonic tests for later reference. For example, after theoperator has performed a test, the microprocessor 78 can prompt theoperator to input information concerning characteristics of the soundproduced in the headphones 26 by displaying a message such as “SoundsLike?” on the display 66. The user would then use the up arrow input key70 and the down arrow input key 68 to scroll through a list of choicessuch as “buzz”, “hiss”, “crackle”, “pop”, “impacting”, etc. Once theuser has located the proper description, the microprocessor 78 can beinstructed to save the description in memory by pressing the mode inputkey 72. It should be readily understood that a variety of otherinformation could be stored using the above described method.

The ultrasonic sensor 22 and the temperature sensor 74 containidentification information that is read by the microprocessor 78 locatedin the elongate housing 24. The identification information is sent by anidentification circuit 23 in the sensors 22 and 74 to the microprocessor78. The microprocessor 78 uses the identification information toconfigure the ultrasonic monitoring system 10 to operate using the typeof sensor 22 installed in the sensor socket 36. The identificationcircuit 23 preferably consist of a memory with a serial output.Preferably, the identification information not only identifies the typeand nature of the sensors 22 and 74, but also includes calibration dataused by the device 10 to accurately interpret the sensors 22 and 74signals.

In an especially preferred embodiment, the identification circuit 23 isa DS2502 1 KBIT Add-Only Memory manufactured by Dallas Semiconductor.Alternatively, the identification circuit 23 is a resistor having aresistance value that corresponds to a particular sensor 22 and 74. Themicroprocessor 78 determines the type of sensor 22 and 74 by determiningthe value of the resistor. In yet another embodiment, the identificationcircuit 23 is a bar graph containing visually encoded information thatis read by an optical sensor located in the sensor socket 36.

The sensor socket 36 is preferably designed to allow the ultrasonicmonitoring system 10 to interchangeably use different types of sensors22. As shown in FIGS. 8a and 8 b, the sensor socket 36 preferablyconsists of a cylindrical chamber 96 for receiving the sensors 22 with aset of electrical contact pins 42 in the bottom of the cylindricalchamber 96 that are in electrical contact with corresponding contactpads 108 on a sensor 22 that has been installed in the sensor socket 36.In an especially preferred embodiment, six pins 42 in the sensor socket36 electrically connect the sensor 22 to the ultrasonic monitoringdevice 10. Two of the pins 42 are used to send the received ultrasonicelectric signals to the voltage controlled amplifier 76 of theheterodyning audio circuit and the received signal strength indicator90. Two pins 42 are used to provide a power supply voltage and a powersupply ground to the installed sensor 22. One of the pins 42 is used toprovide a temperature reading to the temperature sense circuit 92 and,the last pin 42 is used to provide a communication line between theidentification circuit 23 on the sensor and the microprocessor controlcircuit 78 in the elongate housing 24. It is understood that moreelectrical connections could be provided if necessary. Each of the pins42 are spring biased and move axially to yieldably engage the contactpads 108.

The sensors 22 are held in the sensor socket 36 by a pair of protrudingmembers 100 that are designed to be received by corresponding channels98 in the walls of the cylindrical sensor socket 36. In an especiallypreferred embodiment, the channels 98 are L-shaped so that the sensor 22is installed in the sensor socket 36 by inserting the protruding members100 into the top of the L-shaped channels 98 and pushing the protrudingmembers 100 down into the channels 98. The sensor is then twisted sothat the protruding members 100 are securely contained in the leg of theL-shaped channels 98 and prevent the sensor 22 from being removed fromthe sensor socket 36. The process is remotely similar to placing abayonet on the end of a rifle.

The sensor 22 can only be inserted into the sensor socket 36 with theprotrusions 100 on the sensor 22 aligned with the grooves 98 in thesocket 36. Because it is important that the contact pins 42 in thesensor socket 36 be aligned with the proper contact pads 108 of thesensor 22, the protruding members 100 are preferably positioned so thatit is mechanically impossible to install the sensors 22 oriented in thewrong fashion. For example, if the protruding members 100 are placeddirectly across from each other, there are two possible ways to insertthe sensor 22 into the socket 36. Therefore, the protruding members 100are preferably positioned so that they are not directly across from oneanother. This insures that the contact pins 42 in the socket 36 areproperly aligned with the contact pads 108 of the sensor 22. It isunderstood that a number of other mechanical means could be used to keythe sensors 22 to help insure proper insertion, however, theaforementioned approach is easy to implement and quite effective.

A wide variety of ultrasonic sensors 22 can be installed in the sensorsocket 36 depending upon the particular needs of the operator 20. Whileit is appreciated that there are numerous applications for an ultrasonicmonitoring system 10, machinery monitoring and leak detection are theprimary uses for the ultrasonic monitoring system 10 of the presentinvention. The frequency range of interest for these applications isapproximately 20 to 100 kHz. Conventionally, 40 KHz has been used byseveral manufacturers of ultrasonic instruments as the primary frequencyof interest. This is probably the best general purpose frequency range,as it is high enough to be above most loud low frequency machinevibrations yet not so high as to be severely attenuated at reasonabledistances. It should be understood that the ultrasonic sound wavesproduced by machinery defects or leaks typically do not consist of asingle tone or pitch. These sounds are broadband signals that consist ofmany different frequencies. It is the complex nature of the signals thatallows a trained operator to distinguish between the heterodynedultrasonic sounds produced by different conditions. For example, leaksin pressurized containers generally create a rushing sound while arcingand electrical corona typically produce a cracking or buzzing sound. Inaddition to differences in the sounds that can be audibly detected bylistening to the heterodyned signal, a machine analyzer can analyze thefrequency spectrums of the waveforms to detect signal spiking caused bybearing defects or other impact producing conditions. Because of thewide range of applications, it is understood that a variety of differentsensors 22 designed to detect a range of different frequencies could beutilized in accordance with the present invention and the particulartypes of sensors 22 discussed are for illustration purposes only.

Two preferred types of ultrasonic sensors 22 that are utilized with thebayonet style locking system of the present invention are the airborneultrasonic sensor 102, shown in FIGS. 9a, 9 b, and 9 c, and the contactultrasonic sensor 104, shown in FIGS. 10a, 10 b, 10 c, and 10 d. Thepreferred embodiments of both sensors 102 and 104 utilize piezoelectrictransducers 25 to produce ultrasonic electrical signals that correspondto the ultrasonic sound waves reaching the sensors 102 and 104. Theairborne sensor 102 preferably consist of a cylindrical housing 106 witha cylindrical PC board containing six contact pads 108 at one end thatserves to establish electrical connections between the sensor 102 andthe sensor socket 36. In addition, an identification circuit 23 and apiezoelectric transducer 25 are preferably located in the main body ofthe cylindrical housing 106. The piezoelectric transducer 25 is locatedbehind a protective housing 110 in the end of the cylindrical housing106 opposite the PC board containing the contact pads 108. Thepiezoelectric transducer 25 generates ultrasonic electrical signals inresponse to ultrasonic sound waves. The ultrasonic electrical signalsare then split between two inputs on the cylindrical PC board containingthe contact pads 108. The ultrasonic electrical signals are then sentfrom two of the contact pads on the cylindrical PC board 108 to theinput of the received signal strength indicator 90 and the voltagecontrolled amplifier 76.

To allow the operator 20 to determine the precise location of smallleaks or ultrasonic noise sources, a rubber cone 112 with a hole in thetip can be placed over the sensor 102 as shown in FIG. 11. The rubbercone diminishes the ability of the sensor 22 to detect ultrasonic soundsfrom anywhere but the open tip of the cone. Thus, the rubber cone 112permits the operator 20 to more precisely locate a small leak. Materialsother than rubber could be used to construct the cone 112, however, therubber cone 112 does a particularly good job of isolating the ultrasonicsound waves and its flexibility makes it easy to use.

Because each sensor 22 contains identification information, variationsin the airborne ultrasonic sensors 102 are easily accommodated by theultrasonic monitoring system 10. New software can be installed in theultrasonic monitoring system 10 that provides the system with theconfiguration information needed to accommodate the newly developedsensors 22.

The base of the contact sensor 104 is similar to the base of theairborne sensor 102. However, the receiving end of the contact sensor104 consists of a long substantially hollow shaft 114. Ultrasonicvibrations are received by placing the tip hollow shaft 114 of thecontact sensor 104 on the object that is suspected of radiatingultrasonic sound waves. To reinforce and stabilize the shaft 114 of thecontact sensor 104, an adjustable washer 113, that is received bythreads located on the cylindrical housing 106 at the base of the shaft114, is tightened until the contact sensor 104 is firmly held in thesensor socket 36. A piezoelectric transducer 25 is located in the baseof the shaft 114. Placing the tip of the shaft 114 against an objectproducing ultrasonic sound waves causes the piezoelectric transducer 25of the contact sensor 104 to produce ultrasonic electrical signals.While the airborne ultrasonic sensor 102 is mechanically self-resonant,the contact sensor 104 is not. Therefore, the contact sensor 104preferably contains an inductive and capacitive band pass resonantfilter 27 that is preferably tuned to a frequency of 40 KHz. In afashion similar to that of the airborne sensor 102, the ultrasonicelectrical signal is then split and sent to the cylindrical shaped PCboard containing the contact pads 108 that provide electrical contactsto the sensor socket contact pins 42.

The ultrasonic contact sensor 104 preferably contains a temperaturesensor 116 coaxially mounted within the ultrasonic sensing shaft 114.The tip 117 of the temperature sensor 116 is constructed out of amaterial, such as copper, that rapidly conducts heat. A resistance typetemperature detection circuit as shown in FIG. 10d is the preferredapproach to determining the surface temperature of the object beingmonitored. A section of resistance temperature dependent (RTD) material115 is in close contact with the heat conductive tip 117 of thetemperature sensor 116. Thus, the heat conductive tip 117 acts as aconductor of heat between the surface of the object whose temperature isbeing measured and the RTD material 115. The resistance of an RTDmaterial 115 varies relatively rapidly with a change in temperature.Thus, by measuring the resistance of the RTD material 115, a temperaturemeasurement can be obtained. When the temperature sensor 116 is placedin contact with the surface for which a temperature reading is desired,the temperature of the tip 117 changes almost immediately to thetemperature of the surface it is in contact with. The section of RTDmaterial 115 is in close contact with the tip 117 and, thus, alsorapidly changes temperature. In a preferred embodiment using copper forthe heat conducting tip 117 and platinum as the RTD material 115, thetemperature sensor 116 has a time constant response of less than 500milliseconds.

A constant current is supplied to the RTD section of material 115 by thetemperature sense circuit 92. As the temperature of the RTD section 115of the temperature sensor 116 varies, so does the resistance of the RTDsection 115. By supplying a constant current to the RTD material 115, avoltage potential is created across the material 115 that isproportional to the temperature of the sensor tip 117. As thetemperature varies so does the resistance of the section of RTD 115 and,thus, the corresponding voltage potential also varies. By measuring thevoltage potential across the section of RTD material 115 in thetemperature sensor 116, the microprocessor 78 can determine thetemperature of the tip 117 of the temperature sensor 116 and, thus, thesurface temperature of the area in question.

Knowing the surface temperature of an enclosure containing bearings,gears, steam traps, valves, or other machinery provides an indication ofthe condition of the machinery. Temperature information is particularlyuseful when measurements are taken over time and compared. Manymechanical failures result in friction which, in turn, generates heat.Thus, a sudden increase in the surface temperature of a machine tends toindicate a new machinery defect is creating more friction andconsequently more heat. A slow increase in surface temperature mayindicate slowly progressing wear and tear in the machinery. As a furtherexample of how surface temperature might be used to diagnose equipmentfailure, consider steam traps that are used to remove condensate from asteam line. Steam traps usually fail in one of two ways. First, they canfail open, meaning that they remove the condensate but allow steam toescape from the system. Second, they can fail closed, meaning that thepipes become blocked so that no condensate is removed. The temperatureof the exhaust line of a steam trap which has failed open will be veryhigh. Conversely, if the steam trap is blocked, the temperature of thedownstream pipes will be much lower. Therefore, comparing the knowntemperature of a steam trap or machine when it is functioning properlyto its present temperature can provide clues to the device's currentcondition.

The ultrasonic monitoring system 10 further includes an ultrasonic soundwave transmitter 34 that permits the ultrasonic monitoring system 10 tolocate holes in containers that are not producing ultrasonic soundwaves. The ultrasonic sound wave transmitter 34 is turned on and placedinside a pipe, tank, or other sealed environment that it is desired tocheck for leaks. For example, as shown in FIG. 12, the ultrasonic soundwave transmitter 34 can be placed in a sealed environment 118. Once theultrasonic sound wave transmitter 34 is activated, the operator 20 ofthe ultrasonic monitoring system 10 can use the ultrasonic sensor 22 inthe elongate housing 24 to detect any ultrasonic sound waves 12 beingemitted from the ultrasonic sound wave transmitter 34 that are escapingthe sealed environment 118.

One of the primary benefits of using a digitally based ultrasonicmonitoring system 10 that produces referenced decibel signal strengthreadings is the ability to store previously acquired data for laterrecall and analysis. Trending this digitally stored information allowsthe ultrasonic monitoring system 10 to detect changes in a machine'sperformance over time. For example, if the level of ultrasonic noiseemitted by a particular machine dramatically increases from one week toanother, it is highly likely that a machine defect has appeared orworsened in the previous week. In a similar vein, if a machine hasconsistently produced a large amount of ultrasonic noise over anextended period of time without malfunctioning, it is unlikely thatanother reading indicating the machine is producing a large amount ofultrasonic noise is indicative of a problem. Thus, much of theultrasonic data acquired by the ultrasonic monitoring system 10 isprimarily useful when compared to prior data collected under similarcircumstances.

Temperature readings are also much more informative when trended over aperiod of time. For example, a surface temperature reading of 180degrees Fahrenheit may not be particularly revealing in and of itself.However, a series of 120 degree Fahrenheit readings followed by a 180degree reading is much more likely to be indicative of a problem. Thus,trending the data acquired by the ultrasonic monitoring system 10dramatically improves the likelihood of detecting machinery defects.

As briefly mentioned before, the ultrasonic analysis system 10preferably includes a microprocessor based portable personal computer.FIG. 13 is a flow chart showing the steps of a route based method ofmonitoring a series of machines with the ultrasonic monitoring system 10of the present invention. The route based method uses a centralprocessing and storage computer, a portable computer, and a hand heldultrasonic monitoring device. To set up a trendable ultrasonicmonitoring system 10, a brief description of, and the location of, everymachine that is to be monitored with the ultrasonic monitoring system 10is entered into a central processing and storage computer. This step isshown in block 122 of FIG. 13. A monitoring schedule detailing the timesat which each machine should be tested and the tests that should beperformed on each machine is also programmed into the central processingcomputer. In a preferred embodiment, a ten character identification codeis used to represent each machine and a three character identificationcode is used to represent each machine's location. When the time fortesting the machines arrives, the central computer prompts the operatorto download the testing information from the central computer to theportable computer, as shown in block 124. The portable computer examinesthe testing information and prompts the operator to proceed to the firsttesting location in block 126. The method then proceeds to block 128wherein the portable computer loads the testing information needed forthe first test into the hand held ultrasonic monitoring device. Thistesting information includes any configuration data needed for theparticular tests to be performed on the machine. Furthermore, the alarmlevels for the particular machine being tested are automatically sentfrom the portable computer to the hand held ultrasonic monitoringdevice. Thus, the portable computer prompts the operator to go to aparticular location and perform a particular test on a particularmachine and configures the microprocessor control unit in the hand heldultrasonic monitoring device to correctly perform the test. Furthermore,as shown in block 130, the portable computer provides a detaileddescription of how to perform the tests to the operator. It is importantthat the tests be performed in the same manner each time so that theresults of the current test can be accurately compared to the results ofprevious tests. Once the ultrasonic sound wave and temperaturemeasurements have been taken by the operator in block 132, the testresults are downloaded from the hand held ultrasonic device to theportable computer in block 134. In decisional block 136, the portablecomputer must determine whether another test needs to be performed. Ifanother test needs to be performed, the portable computer prompts theoperator to proceed to the next test location and the method returns toblock 128. The software running on the portable computer is preferablyflexible enough to auto increment through a predetermined monitoringroute or receive external inputs, such as bar code information, whichdictate the location in the manufacturing setting to be monitored.However, when all the required tests have been performed, the portablecomputer prompts the operator to download the test results from theportable computer to the central computer. In the final step of themethod depicted in block 142, the central computer compares the testdata from the most recent test to the data from previous tests todetermine the condition of the machines being monitored.

The test results from previous measurements may be used to generatealarm levels for the next series of measurements For example, an alarmlevel can be set so that if the ultrasonic noise level measurement froma particular machine is three decibels higher than the previous theultrasonic noise level measurement an alarm is triggered. The increasein ultrasonic noise from one measurement to the next that is necessaryto trigger an alarm may be varied by the operator depending upon theparticular type of machine being monitored and the circumstancessurrounding its monitoring. Similarly, the current test results may beautomatically compared to predetermined criteria stored in memory todetermine if an alarm situation exists. The predetermined criteria maybe based upon historical or baseline data corresponding to pastmeasurements taken from a particular type machine. In addition, evenmore complex criteria such as the expected ultrasonic sound waveproduction of a particular machine as a function of the amount of timethe machine has been operating are easily accommodated by the routebased system of the present invention.

Depending upon the memory requirements imposed by the number of devicesbeing monitored and the number of tests being performed, the datacontained in the portable computer may not need to be downloaded to apermanent base station. If the storage and processing capacity of acentral computer is not required, the test data may be stored andanalyzed by the portable computer. Furthermore, if sufficient memoryexists in the hand held ultrasonic monitoring device, the hand heldultrasonic monitoring device can perform the steps necessary for a routebased monitoring system.

Storing the ultrasonic electrical signals received from particularmachines also improves the likelihood of detecting a machinery defect bylistening to the heterodyned audio signals produced by the ultrasonicmonitoring system 10. Before the operator of the ultrasonic monitoringsystem 10 listens to the current audio signals produced in response tothe ultrasonic sound waves received from a particular machine, theoperator can prompt the portable computer to playback the audio signalspreviously recorded from the particular machine. This makes it mucheasier for the operator of the ultrasonic monitoring system 10 to detectthe small changes in the audio signals which are often indicative of adeveloping machinery defect.

The ultrasonic monitoring system 10 allows a user to input a number ofconditions that will result in an alarm being generated. These alarmsmay be audible or visual depending on the user's preference. Thesealarms preferably include an alarm for exceeding a user-defined decibellevel, an alarm for exceeding a user-defined temperature level, and analarm to alert the user that the incoming signal is beginning to beclipped by the internal electronic circuitry in the elongate housing 24.

The decibel alarm is defined by accessing the alarm function with themode input key 72 on the elongate housing 24 and using the up 70 anddown 68 arrow input keys to set an alarm limit. Preferably, when thealarm level is reached, an audible alarm is heard in the headphones 26and the referenced decibel readout on the display 66 flashes. The alarmlimit may be triggered differently depending on which operating mode isselected. For example, in the instantaneous, peak hold and peak factormodes, the decibel alarm is preferably activated the first time theincoming signal reaches the user defined limit. However, when in theaverage mode, the decibel alarm is activated the first time the averagereading reaches the user-defined limit.

The temperature alarm is also defined by accessing the temperature alarmfunction with the mode input key 72 and using the up 70 and down 68 andarrow keys to set the alarm limit. When the limit is reached, an audiblealert is heard in the headphones 26 and the temperature readout on thedisplay 66 flashes. The signal clipping alarm indicates the incomingsignal is being clipped and that the user should decrease the volume.The signal clipping alarm can be either an audible alarm in theheadphones 26 or a visual alarm on the display 66.

While the invention has been described in detail, it is to be expresslyunderstood that it will be apparent to persons skilled in the relevantart that the invention may be modified without departing from the spiritof the invention. Various changes of form, design or arrangement may bemade to the invention without departing from the spirit and scope of theinvention. Therefore, the above mentioned description is to beconsidered exemplary, rather than limiting, and the true scope of theinvention is that defined in the following claims.

What is claimed is:
 1. An ultrasonic monitoring device for detectingultrasonic sound waves and vibrations, the device comprising: a housingfor containing the ultrasonic monitoring device in a manner that allowsthe ultrasonic monitoring device to be portably used by an operator; atleast one removable airborne ultrasonic sensor for detecting airborneultrasonic sound waves and producing ultrasonic electrical signalsrelated to said ultrasonic sound waves; at least one removablecontacting ultrasonic sensor for sensing ultrasonic vibrations be beingplaced in contact with an object and producing ultrasonic electricalsignals related to said ultrasonic vibrations; a sensor socket forreceiving at least one of said removable sensors; a digital processingmeans; a split path signal conditioning means comprising a first circuitpath for receiving and conditioning ultrasonic electrical signalswherein a logarithmic amplifier means provides an amplitude demodulatedenvelope of the ultrasonic electrical signals for input to said digitalprocessing means; and a second circuit path for receiving andconditioning ultrasonic electrical signals and providing said ultrasonicelectrical signals to a frequency conversion means for translation toaudible frequency electrical signals; and an output means forcommunicating the results of the digital analysis to a user of thedevice.
 2. The device of claim 1 wherein said removable sensors furthercomprise an information storage means for storing an identificationcode, a zero offset factor, frequency response data, and calibrationdata unique to the particular sensor.
 3. The device of claim 2 whereinsaid output means provide information corresponding to theidentification code stored in the selected sensor.
 4. The device ofclaim 1 wherein said sensor socket further comprises a bayonet stylelocking groove mechanism for retention of said removable sensors.
 5. Thedevice of claim 4 wherein the removable sensors further incorporate atleast one projection or pin for mating with the bayonet locking groovesin the device housing.
 6. The device of claim 5 wherein said sensorsocket further comprises a set of electrical contact pins wherein thecontact pins are spring loaded for connection to said removable sensors.7. The device of claim 1 further comprising a serial communications portfor cabled communication with a computer or data logger.
 8. The deviceof claim 1 further comprising at least one removable temperature sensorfor sensing the temperature of an object and producing electricalsignals corresponding to the temperature of the object.
 9. The device ofclaim 1 further comprising a means for providing a referenced decibelvalue of the ultrasonic sound or the ultrasonic vibrations to the outputmeans.
 10. The device of claim 1 wherein a DC voltage value of anyinstantaneous point of the demodulated envelope corresponds to areferenced decibel value.
 11. The device of claim 1 wherein thefrequency conversion means is a heterodyning circuit.
 12. The device ofclaim 1 wherein said device is a passive device.
 13. An ultrasonicmonitoring device for monitoring ultrasonic sound waves, the devicecomprising: a housing for containing the ultrasonic monitoring device ina manner that allows the ultrasonic monitoring device to be portablyused by an operator; a set of sensors, including at least one of acontact ultrasonic sensor for sensing ultrasonic vibrations by beingplaced in contact with an object producing ultrasonic vibrations, anairborne ultrasonic sensor for sensing ultrasonic sound waves beingproduced by an object without coming into contact with the object and anultrasonic sensor for sensing ultrasonic vibrations having an integraltemperature sensor for sensing temperature of an object, for producingelectrical signals in response to a variety of different conditionswherein each sensor in the set of sensors has a plurality of electricalcontacts; a sensor socket located on the housing of the ultrasonicmonitoring device that is designed to interchangeably and removablyreceive a sensor from the set of sensors wherein the sensor socket has aplurality of electrical contacts for electrically receiving electricalsignals from the plurality of electrical contacts of a sensor installedin the sensor socket and providing the electrical signals from thesensor installed in the sensor socket to the ultrasonic monitoringdevice wherein the ultrasonic monitoring device is passive and eachsensor in the set of sensors contains identification information encodedon the sensor and wherein the ultrasonic monitoring device contains anidentification circuit for receiving and analyzing the identificationinformation from a sensor installed in the sensor socket and configuringthe ultrasonic monitoring device to operate with the sensor installed inthe sensor socket; and a wireless communications port for sending andreceiving signals and for providing properties of the electrical signalsfrom the sensor installed in the sensor socket to an external processingdevice for analysis.
 14. The device of claim 13 further comprising atleast one protrusion fixedly attached to the sides of each of thesensors in the set of sensors wherein the protrusions are shaped andpositioned to be received in at least one groove in the sensor socket ina manner that removably secures the sensor in the sensor socket.
 15. Thedevice of claim 14 wherein the open receiving portion of the at leastone groove is positioned so that the sensors will always be installed inthe sensor socket with the same orientation.
 16. The device of claim 15further comprising installation guide means which prevent a sensor fromthe set of sensors from being improperly installed in the sensor socket.17. The device of claim 13 further comprising focusing means having alarge opening and a small opening such that said large opening fitsaround an installed sensor from the set of sensors and said smallopening receives said ultasonic sound waves such that the area fromwhich the sensors can receive the ultrasonic sound waves is focused. 18.The device of claim 13 further comprising a display for displayingproperties of the electrical signals and displaying identificationinformation concerning the sensor installed in the sensor socket. 19.The apparatus of claim 13 further comprising analysis means forperforming time and frequency domain waveform analysis on the ultrasonicelectrical signals.
 20. The apparatus of claim 13 further comprisingalarm means for indicating when an ultrasonic electrical signal exceedsa user selected threshold value.
 21. An ultrasonic monitoring device formonitoring ultrasonic sound waves, the device comprising: a housing forcontaining the ultrasonic monitoring device in a manner that allows theultrasonic monitoring device to be portably used by an operator; a setof sensors, including at least one of a contact ultrasonic sensor forsensing ultrasonic vibrations by being placed in contact with an objectproducing ultrasonic vibrations and producing electrical signals relatedto said ultrasonic vibrations, and an airborne ultrasonic sensor forsensing ultrasonic sound waves being produced by an object withoutcoming into contact with the object and producing electrical signalsrelated to said ultrasonic sound waves; a sensor socket located on thehousing of the ultrasonic monitoring device that is designed tointerchangeably and removably receive a sensor from the set of sensorswherein the sensor socket has electrical contacts for electricallyreceiving electrical signals from electrical contacts on a sensorinstalled in the sensor socket and configuring said ultrasonicmonitoring device to operate with said sensor installed in the sensorsocket; a digital microprocessor for receiving and processing saidelectrical signals from said sensor socket and producing digital outputdata; and an RS 232 port for receiving said output data from saiddigital microprocessor and outputting said output data to an externaldevice wherein said external device stores said output data and trendssaid output data over a period of time.
 22. The device of claim 21wherein said digital microprocessor is capable of producing a referenceddecibel output based upon said electrical signals from said sensor insaid sensor socket.
 23. The device of claim 21 wherein said digitalmicroprocessor is configured to receive software upgrades provided tosaid RS 232 port from an external source such that said ultrasonicdevice can be configured to process signals from newly designed sensorsinstalled in said sensor socket.
 24. A digital ultrasonic monitoringdevice for monitoring ultrasonic sound waves, the device comprising asensor socket located on a housing of the ultrasonic monitoring devicethat is designed to interchangeably and removably receive a sensor froma set of sensors wherein the sensor socket has electrical contacts forelectrically receiving electrical signals from electrical contacts on asensor installed in the sensor socket and wherein said sensors in saidset of sensors have different sensing properties and wherein each sensorcontains an identification code such that said digital ultrasonicmonitoring device can identify said sensors based upon saididentification code.